This invention relates to a process of recovering monoalkylbenzene and pure 1,3,5-trialkylbenzene from an isomeric mixture of dialkyl- and trialkylbenzenes.
Dialkylbenzenes are useful transalkylating agents in the transalkylation of benzene to valuable monoalkylated benzenes, such as ethylbenzene and cumene. Cumene, also known as isopropylbenzene, is useful for the production of phenol, acetone and alpha-methylstyrene. Ethylbenzene is useful in the production of styrene.
1,3,5-trialkylbenzenes, such as 1,3,5-triisopropylbenzene, are useful as high temperature solvents and as starting materials for the synthesis of agricultural chemicals. 1,3,5-Triethylbenzene is also useful as a starting material for the synthesis of K-resins.
U. S. Pat. No. 4,774,377 discloses the transalkylation of benzene by dialkylated aromatic compounds to monoalkylated aromatic compounds in the presence of an acidic mordenite zeolite catalyst. Disadvantageously, the dialkylated isomer is required to be essentially pure and may not contain significant quantities of trialkylated isomer, because the latter plugs the catalysts' pores and quickly deactivates the catalyst. Accordingly, U.S. Pat. No. 4,774,377 teaches a costly separation via fractional distillation of the trialkylated and dialkylated mixture prior to the transalkylation step.
1,3,5-trialkylbenzenes are prepared by the alkylation of benzene. Catalysts therefor, such as solid phosphoric acid and acidic zeolites, are well known in the art. U.S. Pat. No. 3,761,396, for example, teaches such a process using super-siliceous zeolites as catalysts, such as dealuminated Y, X, L, omega and synthetic mordenite. The examples illustrate the use of these catalysts in the alkylation of benzene with propylene to yield a mixture of mono, di-, and triisopropylbenzenes.
The problem with the above-identified alkylation is that 1,3,5-trialkylbenzene is obtained in a product mixture with 1,2,4-trialkylbenzene and three dialkylbenzene isomers. Typically, the 1,2,3-trialkylated isomer is not obtained in significant quantity. The dialkylbenzenes are usually separated from the trialkylbenzenes by distillation: however, 1,3,5- and 1,2,4-trialkylbenzenes cannot be separated by distillation because their boiling points are too close. Thus, 1,3,5-trialkylbenzene cannot be obtained in high purity by methods known in the art. Moreover, in order to recover the commercial value of the dialkylbenzenes, their isomeric mixture must be separated by further distillation, or alternatively, transalkylated to useful monoalkylbenzenes.
Other syntheses of 1,3,5-trialkylbenzenes have been reported. For example, U.S. Pat. No. 3,268,607 teaches a process comprising contacting benzene with propylene and/or cumene, diisopropylbenzene or triisopropylbenzene in the presence of an acid-activated clay to obtain a product mixture containing predominantly 1,3,5-triisopropylbenzene and 1,2,4,5-tetraisopropylbenzene. The product mixture is cooled to precipitate essentially pure solid 1,2,4,5-tetraisopropylbenzene, which is then separated from the remaining liquid and transalkylated with benzene, cumene or diisopropylbenzene in the presence of the same clay to yield 1,3,5-triisopropylbenzene. Disadvantageously, this process produces large quantities of 1,2,4,5-tetraisopropylbenzene which must be transalkylated back to the more valuable 1,3,5-trialkyl compound.
In view of the above, there remains a need to recover the commercial value of isomeric mixtures of dialkyl- and trialkylbenzenes cheaply and efficiently. Moreover, there remains a need for an effective process of separating 1,3,5-trialkylbenzene from mixtures of the same and at least one of 1,2,4- and/or 1,2,3-trialkylbenzenes.